Posted
by
Soulskillon Tuesday October 19, 2010 @01:07AM
from the water-the-chances dept.

An anonymous reader writes "A team from the Massachusetts Institute of Technology's Field and Space Robotic Laboratory has designed a new solar-powered water desalination system to provide drinking water to disaster zones and disadvantaged parts of the planet. Desalination systems often require a lot of energy and a large infrastructure to support them, but MIT's compact system is able to cope due to its ingenious design. The system's photovoltaic panel is able to generate power for the pump, which in turn pushes undrinkable seawater through a permeable membrane. MIT's prototype can reportedly produce 80 gallons of drinking water per day, depending on weather conditions."

the group built a small prototype [...] the prototype is capable of producing 80 gallons of water a day [...] They estimate that a larger version of the unit, which would cost about $8,000 to construct, could provide about 1,000 gallons of water per day.

So based on your metric this supplies drinking water for over 1000 people. Still need a lot of these for bigger disasters, but $8/person isn't too bad.

Continuing to quote the article: "...The design team also claim that two dozen desalination units could be transported in a single C-130 cargo airplane, providing water for more than 10,000 people."

Think about Haiti in the days after the disaster when clean water was unavailable, the airport was partially inoperable and hopelessly overwhelmed, when airlifting hundreds of thousands of gallons of water (or diesel) was infeasible.

It is for areas of the world where there aren't random creeks (if there were enough random creeks in Haiti, they would be sending water purification tablets and jugs or pots and tea kettles and telling everyone to boil their own water). This is a desalination system, so it can work off of seawater. Industrial scale reverse osmosis desalination plants do exist, showing that there are places where there isn't enough freshwater for the population even in good times.

FTFA 24 of them will fit on a C130 and provide water for "more than 10,000 people", so I'm thinking more like 500 people per large unit and that's under ideal conditions. That's as opposed to a more traditional [usbr.gov] unit about the size of a cargo container that can do 200k gallons a day or enough for 40-50k people. Personally I think for large scale disasters it makes a LOT more sense to drop 2 of those and two fuel/generator sets and supply 10x more people with fresh water since every cargo flight counts.

Reverse osmosis works using permeable membranes - that isn't really the limiting factor since huge reverse osmosis plants exist in a number of places. The issue is that it takes a lot of energy to push water through one of these membranes, and solar probably isn't cutting it.

The system you linked certainly does look impressive. However, it is billed as a water purification rather than a desalination system. Later in the page, it does say that it can handle saline water. Does that mean it can handle seawater, like a reverse osmosis system, or is it designed to work from a river and so its limit is brackish water?

Personally I think for large scale disasters it makes a LOT more sense to drop 2 of those and two fuel/generator sets and supply 10x more people with fresh water since every cargo flight counts.

then you just have to keep air dropping or trucking in diesel every couple days as well. I think the point of it being solar is that it doesn't use up fuel resources which will likely also be quite scarce in a situation like this.

Say the initial tank is good for 2 days, with the initial drop you've provided the equivalent of 20 days with the solar load. If you can't get another fuel drop in in less than 20 days the place is absolutely screwed anyways.

I think your math is wrong - you're saying that people drink 8 gallons of water a day? The figure that always gets thrown around is "drink 8 8oz glasses of water a day", which is 64oz, or half a gallon.

At half a gallon of water per day (which, still, is more than most people drink), that would be 160 people every day getting their recommended amount of water.

Or are you that alienated from the real world that you think people in disasters zones first priority is a daily long hot shower and flushing toilets?

Yes, we use a LOT of water in the west because... well because we can. When the shit hits the fan, 3-5 liters a day can and must be enough. And that is actually a rather liberal amount. Enough to drink, do some cleaning and cook. No it won't give you a life of comfort but guess what, it isn't. It is disaster rel

Brings to mind bushwalking in a remote part of my state. I stuffed up by not taking enough water containers. The walk out happened to be on a cool day. The walk back was at 40C. Two thirds of the way back I was seriously dehydrating. I walked into a shallow lake and drank because I had to. I didn't consider boiling the water. In the future I will.

Gastric infections in the outback are pretty hellish. I struggled to a camping ground and collapsed near a good water tank. I spent the next two of three days (mem

Better then none, and that is also by machine, put 10 machines side by side on the ocean floor all lined up with the same tubing, you can fill those tubes up enough that it spills into a container and keeps the water there for the people, sort of like a water tower....

Pump-fed nanofilters are sort of an old idea at this point. The summary leaves off some critical points like how much it costs and how long the filter lasts.

According to the article, it costs $8000, which is a lot for some things but probably accessible for others. Let's just say it's not going to solve the world's water problem overnight, but it might be handy for relief efforts.

Surfing through to the parent MITnews article [mit.edu], we get a bit more information, but it's still lacking anything about how long the system can operate or what its maintenance costs and requirements are. Does it last a week then you're out most of another $8000? Does it require a lot of technical expertise to maintain? It doesn't say...

Pump-fed nanofilters are sort of an old idea at this point. The summary leaves off some critical points like how much it costs and how long the filter lasts.

Exactly. The panels and pump are probably going to last several years without significant maintenance, but they will need a steady supply of filters to keep the thing going. They could extend the lifetime of them by running them in reverse for some amount of time to clean them out, but you can't do that indefinitely, and the system isn't usable while being back-flushed.

Hi, AC. Since 1000 gallons of water comes out to about 4.2 short tons (1000 gallons * 3785 cc per gallon * 1 g per cc of water / 907185 g per short ton), you would actually get about 29 tons in a week. If you want to round more, 4 x 7 is 28. Congratulations, you can mostly do basic unit conversions. What was your point? Filter cost and maintainability are still major unreported issues. Also, that $8000 doesn't count incidentals - getting the water there, personnel, transportation, distribution.

I don't mean to troll here, but has anyone else noticed that MIT has been producing a lot of things that seem mostly not very interesting? I had a similar thoughts as you, that it's hard to see what is particularly innovative about this. Did they really just fit some solar panels on a standard water filter? Kind of cool, but is it really better than things you'll see in Make?

MIT is a big school. You get all sorts of projects, really. You also get the usual fluff coverage in the media which tells you next to nothing about the actual project.

MAKE also has coverage ranging from some pretty serious projects to "The Most Useless Machine" and "PLCs: What the heck are they" so it might not be a great comparison against all research churned out by a major academic institution. It has great stuff and it usually does a good job of catering to its audience, but at the end of the day it's

This is precisely what I was thinking. The water filter is neat but it is NOT solar-powered. It is electrically powered, and it is in this case coupled with a solar system which provides the power to operate it. I was excited because I would like a better, cheaper solar-powered desalinator.

According to the article, it costs $8000, which is a lot for some things but probably accessible for others. Let's just say it's not going to solve the world's water problem overnight, but it might be handy for relief efforts.

Actually, the 8000$ was the expected cost of a larger 1000 gallon version.

A larger version is also being designed, which will cost $8,000 and will be able to provide 1,000 gallons of water daily.

1000 gallons a day is already a pretty nice amount, but as you said, the maintenance work and costs are unknown.

While this design is a step up, and it certainly must have been a great engineering challenge to build and integrate, there is no groundbreaking technology that goes into this. It's a simple reverse osmosis plant, based on technology that's already being used at commercial scale. The summary is also misleading - this system also requires a lot of energy, it just has a power source with it. In fact, it's almost certainly less efficient than a conventional RO system, both in terms of energy used and embedded

That's what I was thinking - surely a hand pump would be much more useful most of the time? The solar panel would be good for keeping the unit busy when no one's around, but for a portable emergency supply you'd get more useful energy from people winding up a spring using a handle.

It probably depends where, when and how you deploy it - in the immediate vicinity of a disaster, where all hands are already employed with the more immediate task of rescuing trapped/injured people, then having a unit you can stick in the sun and come back to fresh water is probably not a bad thing. Once the immediate danger has passed, it might be more practical to use people power, or to ship in some generators and fuel as an interim solution.

The obvious issue here is cost. But if they can get it low enough, they could sell this virtually anywhere to private residents, and I don't mean just 3rd world countries. Think about places like Australia where they frequently don't have enough water.

We have plenty of water in most places in Australia, however we've just recently started to realise that maybe we shouldn't be wasting so much on things like keeping cars clean and maintaining gardens that are reminiscent of England.

To get the price down, they need production of this. One simple way to do that, is to adopt it to boats in the western world. By doing this, the boats will be able to have clean water on-board available from offshore. Then as production increases, the costs go down. Then it allows these units to be produced CHEAPLY.

Most commercial vessels (cruise ships, cargo/oil tankers, etc) already use evaporative systems (waste heat from engines/generators is used to flash heat water to steam, which is than condensed back into clean drinking water). A possible market would be smaller yachts and sail boats that sail around the Caribbean.

Note the word boat in mine and ship in yours.
For example a 45' viking that is running out of Jupiter is ideal of this. The one advantage of a solar cell approach is that if a boat has an outage (diesel goes out), then you still have water.

Can someone comment on the comparative efficiencies of photovoltaic and solar thermal sources of energy? How much better is this really than using thermal-driven evaporative desalination? I mean, other than lacking in the "new and cool" factor

More's the point, why the hell isn't their a manual pump? You don't need sunlight to hand-crank a piston. Some form of centrifugal brake* will prevent exceeding the maximum pressure of the filter, and it can run indoors with a hose out to the salt water.

* - I don't know if this is the correct term. The faster you turn the crank, a set of weighted brake shoes (or similar) move out towards a high friction surface. The faster you spin, the harder it becomes to continue. Or some such.

To evaporate water already at 100C requires ~41kJ/mol, or 2.3kJ/L. To heat 1L of water from 20C to 100C requires 33.6kJ. So, by this very simplistic model it would require ~34kJ/L to desalinate water by boiling.

Now the efficiency of PV vs thermal in a solar powered system depends on the efficiencies of the collectors. PV is ~25%, at best, solar insolation -> electricity. Heating water to evaporate it is a much more difficult calculation. Basically water doesn't have to be at 100C to evaporate and the losses in a thermal system would increase as the temperature differential (system->ambient) increased but in the end I'm not really educated enough to comment accurately. Hopefully the numbers above will give you some feel for the problem though.

As another poster said, the heat is recovered using heat exchangers. You cool down the desalinated water and brine and heat up the incoming water.
But wait, there's more- every system likes this runs in a vacuum. Water boils at a much lower temperature in a vacuum. Maybe the system runs at 60C instead of 100C.

The problem is that this temperature is too low to kill bacteria and other nasty stuff in the water. So you need to treat with UV and chemicals. This increases complexity of the system slightly

Brilliant!! And to think that nobody who ever was thirsty and living near the sea thought of that! Let's hope the rest of the world reads Slashdot, because there sure are some world-changing insights on it now and then.

Seriously: do the math. How many pans do you need to generate a liter per day? How much time does it take per pan to remove the salt, harvest the water, and insert new water? How much area does all this need?

A lot of these stories make the news not because of their validity, but because they're MIT.

The headline idea has a lots of flaws. For $8000 you can dig a well and install a pump that can supply the water for 250 people. Not only that, you'd have enough money left over to either cover any repair costs for a long time or to put towards another pump. A lot of African villages already have problems with more complex electric pumps, not being able to afford to pay for maintenance so the pumps sit inactive. T

Is reading that hard? DISASTER relief. You can't go around digging wells in a hurry. This system is designed to be put aboard an aircraft and flown to a disaster zone in a hurry to be used until normal operations can be resumed.

It is NOT a permanent solution.

Maybe if you could grasp this from the summary YOU could have gone to MIT and wouldn't be so upset.

What really is so hard to understand about the difference between disaster relief techonology and permanent solutions?

This needs to be set up (need to find a good location, need to assemble it, can't start it working in the night), a steady supply of salt water is needed to feed into it, people need to be trained to clean or change the filters.

This isn't going to be a rapid response system either. A lot of the examples given in the article (desert farmland, Haiti 1 year on) are situations where a medium to long term solution is needed.

The salt doesn't clog an RO filter. Salty water is pumped into the filter, and two streams of water come out, one not salty and one more salty than the input. You dump the more salty water back into the ocean and that's how you get rid of the salt. It gets washed you continuously, actually it doesn't have to: The minerals remain dissolved. The filter will last at least months, probably years.Sure, wells are a more permanent solution, but can you airdrop a water well, and is it producing drinkable water on t

"Ask your favourite well-driller if he'll let you airdrop him into a remote disaster zone to drill a water well today for $8k"

Considering lots of wells are dug by people living in these nations, I'd imagine that if you offered someone $8K ($3K more than the typical cost) for a weeks work (depending on the depth and nature of the well), they'd bite your hand off.

There'd be plenty of money left to transport enough water to last people until the well was ready to use. Alternatively you could just drop a

For $8000 you can dig a well and install a pump that can supply the water for 250 people. Not in a boat, you can't. Nor can you in islands like the Bahamas where there is no salt-free groundwater to pump out. Personally, I think the real market for this is sailing yachts, not disaster relief, but that's just me. As far as the filters, you have a series of filters of decreasing mesh size. The bigger screen filters catch the bigger impurities and are easily cleaned by reversing the flow through them. But I'd

The trick for this application (and I don't know if MIT solved it or not) isn't the concept, which is obvious to almost anyone with an engineering or technical background. Rather, it's the implementation that will make it big. Anyone can hook up a desalinization system to solar cells; what you need to be able to do for this situation is make it cheap, light, mass-producible, rugged, reliable, and easy to operate and maintain.

Actually the project is a testbed for some software algorithms for optimal control of systems in the context of variable power availability (as is the case with solar). Presumably this "smart" controller can achieve significantly higher throughput than a naive approach, for example it can probably optimize the process so that the power-consuming components are operating in their most efficient range over a wide range of input power availability.

What would be really impressive is a hydro-powered desalinization plant. Like you put salt water in the top and out the bottom comes fresh water, and the extract goes into a bucket which you can sell to saltwater aquarium enthusiasts.

The photo of the unit shows what appears to be a Clark Pump as used in Spectra Watermaker systems. (http://www.spectrawatermakers.com [spectrawatermakers.com]) These are popular in recreation long distance sailboats as they require less power for a given output than traditional RO systems.

As for reliability and longevity, much depends on the design. If you keep pressures reasonable, and flow excess raw water back to its source, the RO membranes will last many years and thousands of hours of use. The key is not running pressures so high that the membrane gets clogged with solids from the raw water. Pre filtering the raw water also is critical to not fouling the membranes. We run a 30 micron then 10 micron filter before out high pressure pump. The prefilters only need to be changed when fouled so their life span depends on the turbidity of the raw water.

We live aboard our boat and run a watermaker instead of using shoreside water sources. The unit is not as energy efficient as the MIT units. We have used it for years, have over 500 hours on it, and it has had near zero maintenance. In cold water, currently seawater is about 48F, we get 15gph, at 55F+ we get 18gph which is the max rated output, and above that we need to run at lower pressures to not saturate the membrane. We can get greater throughput by adding additional membranes. Adding a second membrane would double our output. (Sorry for the non metric units.) The Clark Pump system will get lower output, but the longevity of the membranes should be comparable. Membrane prices vary, but are typically in the US$250-US$500 range.

Spectra has been selling a "Solar Cube" [spectrawatermakers.com] system for years now, which seems to be just what these folks from MIT are making. Same application and everything. I wonder how different the MIT thing is.

The moment I read Solar PV I knew these guys had lost the plot. Why on earth do we need it to even have a pump, let alone moving parts and a costly Solar PV array to power it? If it's a big enough emergency, dump thousands of "Life Straws" [vestergaard-frandsen.com] into the field and let the wonder of the human mouth suck the water through the straw directly from the river, which filters it by the time it hits the lips. Solar PV? Are they trying to kill people by making this more expensive than it has to be? The Life Straw is also m